President Donald Trump has accused his predecessor, former President Barack Obama, of tapping the phone lines at Trump Tower before the November election. The unprecedented accusation has raised a lot of eyebrows in Washington, across the country and around the world.

President Donald Trump has accused his predecessor, former President Barack Obama, of tapping the phone lines at Trump Tower before the November election. The unprecedented accusation has raised a lot of eyebrows in Washington, across the country and around the world.

House Intelligence Chairman Devin Nunes — a Trump supporter and member of Trump’s transition team — made a peculiar statement this week, presumably in defense of Trump. He told reporters, "A lot of the things he says (Trump), you guys take literally."

Here is what Trump tweeted Saturday morning at 6:30 a.m.: Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!

Is there anything ambiguous about that statement? Could President Obama have ordered a wiretap of candidate Trump or his campaign headquarters?

In order to legally tap a phone line the government needs a warrant. Obviously, an illegal wiretap — by its very nature — does not involve a warrant.

Why is a warrant required to put a wiretap in place? The U.S. Constitution provides that people should be secure in their homes from unlawful searches. Specifically, the Fourth Amendment provides:

"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."

The Founding Fathers did not consider the possibility of electronic communications when they wrote those words.

The U.S. Supreme Court ruled in 1928 that listening in on a phone conversation was not an illegal search because police did not actually enter into the suspect’s home. It was not until 1967 that the high court acknowledged that a person on the phone, albeit in a phone booth with the door closed, had a reasonable expectation of privacy.

Today, people have an expectation of privacy in their homes and offices with regard to telephone conversations unless the government obtains a warrant.

How does that work?

The law authorizing federal criminal wiretaps is Title III of the Omnibus Crime Control and Safe Streets Act of 1968. The federal law, as well as the law in all 50 states, requires probable cause.

Probable cause is a reasonable belief that a person has committed or will commit a crime. For probable cause to exist, a law enforcement officer must have sufficient knowledge of facts to warrant a belief that a suspect is committing a crime. The belief must be based on factual evidence, not simply on suspicion.

During a criminal investigation a prosecutor goes before a neutral judge with an affidavit of probable cause and asks for a search warrant. If the judge is satisfied that probable cause exists the warrant is issued.

In a national security case, the FBI and attorneys in the Justice Department’s National Security Division prepare a declaration laying out the grounds for seeking an order from the Foreign Intelligence Surveillance Court commonly referred to as the "FISA Court." FISA is a secret tribunal with legal authority to review warrants for electronic surveillance against suspected spies or terrorists.

The FISA Court is made up of 11 federal judges selected by the chief justice of the Supreme Court, serving seven-year terms, reported the Washington Post. The court routinely meets in private and the applications for court orders and the actual orders remain highly classified.

A senior intelligence official, typically the FBI or CIA director, must certify to the court that the purpose is to collect foreign intelligence and that the information cannot be obtained by normal investigative means.

The application must be approved by either the attorney general, the deputy attorney general or the head of the National Security Division.

Missing from the federal criminal court rules and the FISA Court rules is the direct input of the President--because, contrary to the opinion of President Trump--Presidents neither order nor apply for search warrants or wiretaps.

Matthew T. Mangino is of counsel with Luxenberg, Garbett, Kelly & George P.C. His book “The Executioner’s Toll, 2010” was released by McFarland Publishing. You can reach him at www.mattmangino.com and follow him on Twitter at @MatthewTMangino.